Iowa Code § 637.607

The fair market value of the trust shall be determined at least annually, using such valuation date or dates or averages of valuation dates as are deemed appropriate. Assets for which a fair market value cannot be readily ascertained shall be valued using such valuation methods as are deemed reasonable and appropriate. Such assets may be excluded from valuation, provided all income received with respect to such assets is distributed to the extent distributable in accordance with the terms of the governing instrument.